🚀 go-pugleaf

In article <sVq7wB2w165w@sys6626.bison.mb.ca> flux@sys6626.bison.mb.ca (John Kamchen) writes:
>I am looking for a circuit that can provide me with a 14.318318Mhz
>pixel clock, derived from an incomming video source.
>I'm using an LM1881 video sync separator to obtain the needed sync 
>signals.

Well you could do it the same way TVs do:  Use a crystal oscillator
phase-locked loop.  That is, instead of using a VCO, use a crystal
oscillator with a variactor diode to adjust the crystal frequency a little.
Use some type of charge-pump circuit to get the control voltage for the
diode, and only enable the pump-up and pump-down signals during burst-gate
from the 1881.  See any color TV schematic.

Have you tried a 74S124 VCO?  That should be stable enough if you power the
analog side of it with its own 7805.  Also make sure no high-frequency noise
can get into the control signals.  Parallel the PLL filter with small disk
capacitors.

Also there is supposedly a difference between signetics and ti versions of
the 74S124.  The signetics version was supposed to be the best.

A few days ago someone posted another good method:  Use a low-distortion
transistor sine-wave oscillator for a VCO.

Tonight I'm going to attempt to build a PLL for deriving the dot-clock from
the H-sync signal of a computer-generated video source.  Its for a b/w video
capture board for obtaining data from medical imaging equipment (the
computers for CAT scanners and MRI machines unfortunately don't allow users
to download the image directly, so you have to capture it from the video
output to the monitor.  Also there's no standard video signal they use, so
you have to handle any video format).  So I'm about to have this same
problem.

BTW, what good wideband flash A/D convertors have people seen?  I'm using an
ADC-304 from DATEL, but they're expensive and the ADC-304 is speced only up to
8MHz bandwidth and 20Mhz sample rate.  Their 1988 catalogue lists better
ones, (like the ADC-301 which is 15MHz bandwidth and 30MHz sample rate) but
they're ECL, have high capacitance inputs and the salesperson says that
ADC-301 - ADC-303 are discontinued.

Also are any fast acquisition time sample & hold circuits available?  I'm
digitizing a periodic signal, so the capturing doesn't have to be real-time.
How difficult would it be to make a fast diode-switch sampler (as in a
mixer), using an LH0033 as a driver?
-- 
/*  jhallen@world.std.com (192.74.137.5) */               /* Joseph H. Allen */
int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--;)q=3&(r=time(0)
+r*57)/7,q=q?q-1?q-2?1-p%79?-1:0:p%79-77?1:0:p<1659?79:0:p>158?-79:0,q?!a[p+q*2
]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817;)printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);}